UNLABELLED: Nonabsorbable disaccharides (NADs) have been used to treat hepatic encephalopathy (HE) since 1966. However, a Cochrane Review, published in 2004, found insufficient evidence to recommend their use in this context. This updated systematic review evaluates the effects of the NADs, lactulose and lactitol, for the treatment and prevention of HE in patients with cirrhosis. Thirty-eight randomized controlled trials, involving 1,828 patients, were identified through electronic and manual searches; 31 randomized controlled trials looked at the treatment of HE, while seven looked at its primary/secondary prevention. Random-effects meta-analyses showed that, compared to placebo/no intervention, NADs had a beneficial effect on HE (relative risk [RR] = 0.63, 95% confidence interval [CI] 0.53-0.74, number needed to treat [NNT] = 4) and serious liver-related adverse events such as liver failure, variceal bleeding, serious infections, spontaneous bacterial peritonitis, and hepatorenal syndrome (RR = 0.42, 95% CI 0.26-0.69, NNT = 50). Treatment was also associated with a reduction in mortality in patients with overt HE (RR = 0.36, 95% CI 0.14-0.94, NNT = 20), although not in patients with minimal HE. Meta-analyses of the prevention randomized controlled trials showed that NADs prevented the development of HE (RR = 0.47, 95% CI 0.33-0.68, NNT = 6), the risk of developing serious liver-related adverse events (RR = 0.48, 95% CI 0.33-0.70, NNT = 6), and reduced mortality (RR = 0.63, 95% CI 0.40-0.98, NNT = 20). Use of NADs was associated with nonserious gastrointestinal adverse events. There were no differences in the efficacy or safety of lactulose and lactitol. CONCLUSIONS: NADs have beneficial effects in the treatment and prevention of HE; their use, in this context, confers additional benefits including a reduction in serious liver-related morbidities and all-cause mortality. (Hepatology 2016;64:908-922).